The rat cell is a non-permissive host for the replication of avian sarcoma virus (ASV). Infectious progeny are not released but viral expression can occur. Rat fibroblasts will be exposed to ASV. Virus-infected cells expressing different biological properties will be isolated and used to prepare clonal populations. Attempts will be made to isolate clones with the following phenotypes: (1) transformed, (2) non-transformed but expressing viral RNA, (3) non-transformed, not expressing viral RNA but containing viral DNA. Morphological revertants of the transformed clones will be isolated. Several independent reversion events from a single transformed clone will be characterized biologically. Each of the clonal populations will be examined using site-specific endonuclease analysis of the chromosomal DNA so that the arrangement and location of the integrated ASV DNA sequences can be determined. The viral-specific RNA will be isolated and analyzed with respect to amount, size and genetic composition using gel electrophoresis and hybridization. An understanding of both the viral-specific RNA metabolism and the nature of the interaction of the viral DNA with the cellular DNA within different clonal populations should provide information concerning: (1) the interaction of ASV in a non-permissive host that is susceptible to transformation and (2) the nature of reversion in that host.